1. Field of the Invention
This invention relates to a piezoelectric ceramic composition not containing lead in the composition, its production method, and a piezoelectric device using the piezoelectric ceramic composition as its material.
2. Description of the Related Art
A PZT (PbTiO3–PbZrO3) component system ceramic containing lead has been used in the past as a piezoelectric ceramic composition.
PZT described above is excellent in an electro-mechanical coupling coefficient and in piezoelectric characteristics such as a piezoelectric constant, and piezoelectric devices utilizing PZT have been widely used in sensors, actuators, filters, and so forth.
Though having excellent characteristics, the piezoelectric ceramic composition formed of PZT contains lead as one of its constituent elements. Therefore, detrimental lead is likely to elute from industrial wastes of products containing PZT and to induce environmental pollution. Concerns about the environment in recent years have made it difficult to produce those products that may result in the environmental pollution such as PZT. Therefore, development of piezoelectric ceramic compositions not containing lead has been required, and a piezoelectric ceramic composition expressed by the general formula (K1-xNax)NbO3 (with the proviso that 0<x<1) has drawn increased attention (“Journal of the American Ceramics Society”, 1962, Vol. 45, No. 5, p209).
However, because sintering of the piezoelectric ceramic composition expressed by the general formula (K1-xNax) NbO3 (with the proviso that 0<x<1) described above is difficult, hot-press sintering must be conducted and the cost of production becomes high. The piezoelectric ceramic composition has a low mechanical quality coefficient Qm and a large dielectric loss. As the piezoelectric ceramic composition according to the prior art has a low piezoelectric d31 constant and a low electro-mechanical coupling coefficient Kp, its application to piezoelectric devices such as piezoelectric filters, piezoelectric vibrators, piezoelectric transformers, piezoelectric ultrasonic motors, piezoelectric gyro sensors, knock sensors, etc, that require a high piezoelectric d31 constant and a high electro-mechanical coupling coefficient Kp has been difficult.
Therefore, though the piezoelectric ceramic composition expressed by the general formula (K1-xNax) NbO3 (with the proviso that 0<x<1) is believed to be a promising novel composition that will replace PZT, it has hardly been put into practical application. For this reason, a lead type piezoelectric ceramic composition, such as PZT, that may invite the environmental pollution, is still utilized widely at present even though the piezoelectric ceramic composition expressed by the general formula described above has been developed.